The clip fasteners are used in the automobile industry to attach and assemble moldings, trim pieces and other components to panels and other such members. In the electronic and communications industry, the clip fasteners are used to assemble and attach electronic chassis assemblies to support structures, such as equipment racks and cabinets.
The fasteners are formed with retaining tabs which are sheared and formed from side legs, so when the fastener legs are inserted in a work piece opening, the tabs resiliently engage the edges of the opening to retain the fastener in place. A screw extending through a second work piece is turned down through an aperture in the fastener to mechanically join the two work pieces. Such fasteners are described for example, in U.S. Pat. Nos. 4,595,325 and 3,795,890. Another example of the use of retaining tabs sheared and formed from side legs is described in U.S. Pat. No. 3,645,311.
The clip fasteners of this general type have been intended for securement to relatively rigid work pieces or members made of metal or plastic. In order to prevent the fastener from turning relative to the work piece when torque is applied to the screw used to join the two work pieces, the work piece opening receiving the fastener is made rectangular or given some other irregular shape or the fastener and work piece are provided with abutting shoulders. U.S. Pat. No. 4,798,507 to Olah (1989), Sheet Metal U-nut, is an example of a fastener abutting the work piece. The U-nut clips into an opening in the work piece spaced at a specific distance from the edge. The edge of the work piece abuts the U-nut hinge surface and prevents the U-nut from turning. U.S. Pat. No. 4,595,325 to Moran (1984) is a fastener of the general type requiring a rectangular opening on the work piece to prevent the fastener from turning relative to the work piece when torque is applied to the screw used to join the two work pieces.
Fasteners of the general type requiring to be installed in a rectangular opening on the work piece are limited in their scope of application and use. The rectangular opening is usually of a unique shape that requires the use of a special sheet metal punch and die-set to form it. In a high volume production environment it is very undesirable to use rectangular shaped metal punches because the sharp corners wear out quickly and therefore the opening produced fails to meet its dimensional specifications. The parts produced are rejected and production is suspended while the die-sets are replaced. Another unfavorable factor is the high levels of stress concentration at the sharp corners of the opening, which under a vibration environment cause the sheet metal to fatigue and crack open, causing the strength of the joint to weaken and the fastener to lose its grip on the work piece. The same mode of failure occurs on a rectangular opening in a plastic panel. On an automobile, exposed to weather and the elements, the cracked sheet metal corrodes and the integrity of the of the entire automobile is deteriorated.
U.S. Pat. No. 5,176,482 to Reinl (1993) discloses a mounting assembly for motor vehicles. It discloses a sheet metal nut held in a restricted and readily movable manner on the body sheet of an automobile, by two rectangular mounting openings and adjacent lateral beads. The construction is to insure that considerable tolerance accumulation between the position of the openings on the body sheet, the position of the fastener and the position of the component opening can be accommodated. The operation of the fastener requires a unique and complex preparation of the body sheet with two rectangular openings plus two special shape beads formed on the body sheet. The rectangular openings accommodates some amount of tolerance accumulation in vertical direction and in a horizontal direction, but if the opening were made round with a diameter equal to the diagonal distance between the corners of the rectangular opening, the round opening would accommodate a larger tolerance accumulation by allowing the fastener to move all-around in a diametrical manner.
U.S. Pat. No. 4,300,865 to Murray (1981) discloses a blind clip fastener for anchoring into a round hole. An object of the invention was to provide a fastener of this type particularly suitable for securement to members or panels made of relatively of soft material such as sheet molded fiberglass compounds. The fastener resists turning when seated in a round hole by driving its sharp edges into the soft material. This is a fastener intended for a limited application, as described in its disclosure. It can not be used on sheet metal panels or hard plastic parts because it would turn under the torque applied to a screw. The fastener is also intended to be used to support light pieces, such as trims and moldings, because it only has a single thread helix formed on its head. Multiple threads are formed or tapped on fasteners which are required to withstand the higher torque values applied to screws supporting large panels and components.
A snap-in Teenut.RTM. fastener manufactured by American Engineered Components, Inc., Cambridge, Mass. is a fastener with tabs or pawls sheared and formed from side legs in a similar manner as described in U.S. Pat. No. 3,645,311 and with a sleeve drawn from its top portion and threaded internally. The Teenut.RTM. is designed to snap into a rectangular hole to prevent it from turning relative to the work piece; it is not provided with anti-vibration features to grip and adjust to variations in material thickness; it is not provided with features to accommodate accumulation of tolerances; it is not provided with a feature to induce a locking torque on the threads and to prevent the engaged screw from turning loose.
All the fasteners known suffer from a number of disadvantages:
a) The single formed screw thread on the head of many fasteners limits the amount of torque the fastener can withstand and the amount of holding force it can applied to the work piece. The capacity of the holding screw is also limited by the single formed screw thread on the head of the fastener. PA1 b) The need of a rectangular opening or an irregular shape opening to prevent the fastener from turning is a structural integrity issue and a product reliability issue. The need of a special punch and die-set for fabrication of the work piece is a manufacturing issue and concern. PA1 c) The U-nut type of fastener is limited by its need to be installed abutting the edge of a panel. It can not easily be installed inside an existing panel. The Reinl's fastener is a U-nut type fastener mounted inside a panel in a complex set of rectangular openings and formed or embossed beads. PA1 d) The clip fasteners are restricted in their use by only large manufacturing facilities who have access to the machine tools and the punches used to form the special shape openings required for their installation. The general public can not use these fasteners simply because the tools required for their installation are not readily available and easy to use. PA1 a) to provide an improved blind snap mounted clip fastener. PA1 b) to provide a clip fastener for anchoring into a round hole. PA1 c) to provide such a fastener which resists turning when seated in a round hole by means of a simple feature that prevents it from turning relative to the work piece. PA1 d) to provide a fastener of this general type which is easy to install by anyone with simple home tools. PA1 e) to provide a fastener with a combination self-locking and anti-vibration feature. PA1 f) to provide a fastener which is suitable for securement to members made of sheet metal or molded plastic. PA1 g) to provide a blind clip fastener which can tolerate dimensional variations in the thickness of the panel in which it is seated. PA1 h) to provide a blind clip fastener which can accommodate considerable tolerance accumulation between the position of the fastener, work piece and the position of the opening on the component to be secured. PA1 i) to provide a fastener able to provide and withstand established industry standard torque values for threaded fasteners. PA1 j) to provide a blind clip fastener which is relatively easy and inexpensive to manufacture.
The need exists for a low cost, blind snap mounted clip fastener for anchoring into a round hole, that is simple to manufacture, that is easy to use, that is provided with a simple feature that prevents it from rotating relative to the work piece and in combination with other features, such as prevailing torque, self-locking and multiple engaging threads. The need exist for a fastener of this general type be available to the general public and anyone who possesses simple home tools, such as a drill can install and use to satisfy a personal need.